The World Cup starts right here. With seven months to go before the death-by-samba opening notes of Brazil 2014, the scheduling may suggest otherwise. But sometimes you just have to go with these things and from the moment Portugal and Sweden were drawn together in Europe's World Cup qualifying play-offs the prospect of Cristiano Ronaldo and Zlatan Ibrahimovic in a final eliminator to decide which of these club football behemoths gets to play at Brazil 2014 was always likely to be less of a subplot and more an unignorable prologue.

Zlat-Ron One – otherwise know as the first leg of Portugal versus Sweden – takes place on Friday night in Lisbon, with the second leg in Stockholm on Tuesday. As an event it already feels not so much like a meeting of nations, as a multilayered collision of interests. On Thursday morning the front cover of Lisbon's sports daily A Bola carried a giant graphic of Ronaldo's head morphed – with surprising ease: both objects are slick, shiny and oddly alluring – into the World Cup trophy itself, alongside the words: "Portugal has the best in the world, and the World Cup wants him there!"

The second part, at least, is unarguably true. Albeit in a sport increasingly entwined around the violently all-pervasive marketing of its top stars, there is another side to this. If the absence of Ronaldo would be a disaster not just for Portugal but for the global diaspora of international Ronaldo-philes, not to mention Nike, Coca-Cola, Castrol, Herbalife and KFC, we must also spare a thought here not just for Sweden, but for Xbox, Bonnier, and the mob-handed cross-border nation of Zlatan. Little wonder, then, that the World Cup starts here. It has no real choice in the matter.

Plus of course, there is the football. This is above all a deliciously moreish collision of two of the great attacking players of the age. Erik Hamren, Sweden's manager, has already had his say on this one, declaring at his pre-match press conference in Lisbon that he has already voted for his captain in the Ballon D'Or. "Ibrahimovic is my player, he is my captain and he is my No1," said Hamren. And if there has been a temptation all round to get down straight away to the brass tacks of Zlatan v Cristiano, then there is also some wider justification for this. These are two evenly matched teams, with a similarity in style, too, given Hamren's attempts to impose a more possession-based game on Sweden.

Both have a convincing defence and one attacking ace (Ibrahimovic has 20 international goals in the past two years to Ronaldo's 17). If Portugal are narrow favourites this is a reflection of the fact that it is Ronaldo who undoubtedly shades it in the modern attacking greats stakes. If this is an essentially irresolvable comparison, it is also an illuminating one. Ronaldo and Ibrahimovic have helped define not simply the conversation around football but also the way it is now played at the highest level. They are similar in lots of ways, bulked up and aggressively processed – but still recognisably street-football kids of a type that seemed likely to vanish from elite football a decade ago.

Both are perhaps beneficiaries of what has been called the Ronaldinho effect, the Brazilian's success at Barcelona the most obvious driver of a wider acceptance that the ability to beat an opponent with an off-the-cuff piece of skill can be the most effective way of countering the relentless athleticism and defensive pressing of opponents at the highest level. Helped by changes in refereeing, a degree of individualism has crept back into top level football. Albeit of the two on show here, it is Ronaldo's sheer mechanical relentlessness that makes him the more effective player. Ibrahimovic remains essentially a "flashbulb footballer", able to decide a match through a burst of explosive inspiration. In effect his career is a series of these supremely effective moments – moments that are often beyond any other footballer, such is his combination of gymnasticism, physical heft and extreme inventive technique. This has led some in England to label him a gadfly and a YouTube player, but this is to miss the point.

As he wrote in his autobiography I Am Zlatan: "I save my energy so I can burst out with fast aggressive moves." He flickers. He does it a lot. Against good teams. It is simply a way of winning.

Ronaldo, by contrast, is a more relentless figure, a one-man termite invasion of a brilliantly gifted footballer. Where Zlatan plays like he could kill you if he wanted to, but he's just going to wait until he's ready, Cristiano plays like he wants to kill you every second of the day. He is, in effect, a kind of footballing terminator. You cannot call him off. He will keep coming. And in the end, you will crumble. For this reason his numbers are frankly astonishing: the first European player in a leading league to score 40 goals in two consecutive seasons, the Real Madrid player to reach 100 league goals in the least time and now past the 300 mark.

Only Lionel Messi, who is another story altogether, can match him. For this reason you can just about – squint a little, ignore the heresy – imagine Ronaldo doing a Maradona at a World Cup and overwhelming teams in the late stages with his individual momentum. Ibrahimovic, not so much. It is a more or less meaningless distinction, but a distinction nonetheless.

More interesting than this are the points where they converge. For all their technical invention both are thrillingly powerful physical specimens. It is a quality Ronaldo honed in the Premier League and then under José Mourinho, instigator of his current gilded battering ram central role. Ibrahimovic bulked up under Fabio Capello at Inter, where he was told to focus not on the "nice" football of his Ajax days but on power and directness.

Beyond this there are personal similarities. There is a kind of revenge-of-the-nerds quality to both men. The young Ronaldo was a skinny kid with bad teeth and bad skin, a Madeiran mocked at one time by Mourinho for his island accent and manners. Raised in poverty in a suburb of Malmo, Ibrahimovic was a scrawny outsider, a bicycle thief with a brain. And it is here that something of the basic anachronism of international football begins to insert itself.

For Zlatan outsiderdom comes in part from a question of nationality. An immigrant Swede displaced by the collapse of Yugoslavia, he has described himself as "un-Swedish" and "a typical bloody Yugo", while one of the oddities of his autobiography is his apparent lack of interest in the Sweden team. More attention is paid to his struggles to get hold of an Enzo Ferrari ("There was a long waiting list – what were we going to do?") than his struggles at the 2006 World Cup the same year while the entire 2002 tournament gets less page time than a nightclub fight that happened just after it.

Perhaps in the end it is best to see Sweden's star player as an inhabitant simply of Zlatan-ville, a canton of that floating sporting super-state now moored around the Champions League and Europe's grandest big city clubs. Ibrahimovic, Ronaldo – and also Messi – have been peripheral at international tournaments, their claims to sporting ultimacy driven so far by individual feats in European club football. For Ronaldo, at 28, and Ibrahimovic, four years older, this is perhaps a final opportunity to change this dynamic.

"The team is what matters," Ibrahimovic said on Wednesday, soft-pedalling the notion of a personal duel. And the contest between the two teams is just as finely poised. Sweden are in the process of a stylistic regearing begun before Euro 2012, a rejection – sorry, Mr Hodgson – of the pragmatic Swedish football of the past 20 years.

It is no doubt galling that this process has been hampered by a lack of wider technical talent. For Sweden there are no obvious Zlatans-in-waiting. The new urban population has produced a generation of ethnic immigrant players for the under-21s but none as yet with Ibrahimovic's outstanding street football gifts. For Portugal the story is similar: they remain in outline Cristiano and 10 other adept but non‑stellar footballers.

With this in mind, and ignoring the battle of the brands, it is by no means a wider sporting tragedy that one of these modern colossi must miss the World Cup finals. Instead it could be seen as confirmation of the basic meritocracy elite level football. Great players have missed World Cups before. George Best never made it. Kevin Keegan was a two-times European footballer of the year before he played at in one. Football is not wrestling. For all the corporate interests it is still pure sport with all its glorious uncertainties, as events Friday into Tuesday in Lisbon and Stockholm will demonstrate.

Ronaldo and Ibrahimovic, distant all-star brothers in arms, have both delivered at last-ditch qualification hurdles in the past. Now one must miss out. And football, whatever the outcome, is perhaps all the richer for it.